1. Field of the Invention
The disclosures herein generally relate to an electromechanical conversion element, a liquid drip discharge head and an image forming apparatus. Especially, the present invention relates to an electromechanical conversion element including an electromechanical conversion film formed of a piezoelectric body, a liquid drip discharge head provided with the electromechanical conversion element and an image forming apparatus provided with the liquid drop discharge head.
2. Description of the Related Art
Conventionally, liquid drop discharge apparatuses, each having a liquid drop discharge head that discharges a liquid drop of ink which is liquid for forming an image, as image forming apparatuses such as printers, facsimile machines or copy machines, have been known. The above-described liquid drop discharge head includes a nozzle for discharging liquid drops, a liquid chamber communicating with the nozzle, and a pressure generation unit that generates a pressure to be applied to liquid in the liquid chamber. As the pressure generation unit, for example, a unit in which on a vibration plate serving as a part of a wall surface of the liquid chamber, a piezoelectric type electromechanical conversion element having an electromechanical conversion film formed of a piezoelectric body is provided, has been known. According to deformation of the electromechanical conversion element by applying an electric voltage, a surface of the vibration plate on the side of the liquid chamber, on which the electromechanical conversion element is provided, is displaced, and thereby a pressure to be applied to liquid in the liquid chamber can be generated.
As the above-described electromechanical conversion element, a configuration in which a lower electrode, an electromechanical conversion film, an upper electrode and the like are laminated has been known. As a material of the above-described electromechanical conversion film, a material having a perovskite crystal structure, such as lead zirconate titanate (PZT), has been generally used. The electromechanical conversion film having the perovskite crystal structure is a ferromagnetic material having a spontaneous polarization property. In the ferromagnetic material, in the case where a direction of a spontaneous polarization axis is caused to coincide with a direction of an electric field, a strain displacement extending in the direction of the spontaneous polarization axis (strain displacement by the piezoelectric effect) can be obtained.
Japanese Published Patent Application No. 2008-192868 describes that in the electromechanical conversion film having the perovskite crystal structure, the strain displacement according to a piezoelectric effect of the above-described electromechanical conversion element can be made greater by making a crystal orientation of a (100) plane higher (a crystal orientation rate is greater than or equal to 80%), aligning directions of the spontaneous polarization axes and forming an electric field in the above-described direction. Moreover, Japanese Published Patent Application No. 2008-192868 describes that in the electromechanical conversion film, the strain displacement of the above-described electromechanical conversion element can be made further greater by rotating a polarization domain and using an effect of the rotation of the domain. The polarization domain refers to a region where the directions of the spontaneous polarization axes are aligned in the electromechanical conversion film.
Furthermore, it is experimentally known that in order to increase the above-described strain displacement it is effective to make a shape of a peak of diffraction intensity asymmetric, which is obtained from a plane parallel to a plane preferentially oriented according to a measurement by θ-2θ method in the electromechanical conversion film having the above-described perovskite crystal structure. Meanwhile, the peak of the diffraction intensity refers to a convex part of a diffraction intensity curve obtained by measurement.
However, it is found that in the electromechanical conversion film having the above-described perovskite crystal structure, even if the shape of the peak of the diffraction intensity obtained from the plane parallel to the plane preferentially oriented according to the measurement by the θ-2θ method is made to be an asymmetric shape, the strain displacement cannot be made sufficiently great.
In the above-described electromechanical conversion film having the perovskite crystal structure, a measurement by the rocking curve method along with the θ-2θ method is often used in order to evaluate a crystal orientation. The inventors of the present application have found that at a position where diffraction intensity becomes the maximum in the measurement by the θ-2θ method, a shape of a peak of the diffraction intensity obtained by the measurement by the rocking curve method becomes an important criterion for increasing stress displacement.
Furthermore, in the analysis of a crystal structure of the above-described electromechanical conversion film having the perovskite crystal structure, in order to evaluate how much a crystal plane is tilted with respect to a substrate plane, a measurement of changing a tilt angle is performed in a peak of diffraction intensity at a position where the diffraction intensity becomes the maximum (2θ). The inventors of the present application have found that a shape of the peak of the diffraction intensity obtained by the measurement of changing the tilt angle (χ) becomes an important criterion for increasing the stress displacement.